The present invention relates to electrochromic devices and more particularly relates to solid-state, inorganic thin film devices.
Electrochromic materials and devices have been developed as an alternative to passive coating materials for light and heat management in building and vehicle windows. In contrast to passive coating materials, electrochromic devices employ materials capable of reversibly altering their optical properties following electrochemical oxidation and reduction in response to an applied potential. The optical modulation is the result of the simultaneous insertion and extraction of electrons and charge compensating ions in the electrochemical material lattice.
In general, electrochromic devices (“EC devices”) have a composite structure through which the transmittance of light can be modulated. FIG. 1 illustrates a typical five layer solid-state electrochromic device in cross-section having the five following superimposed layers: an electrochromic electrode layer (“EC”) 14 which produces a change in absorption or reflection upon oxidation or reduction; an ion conductor layer (“IC”) 13 which functionally replaces an electrolyte, allowing the passage of ions while blocking electronic current; a counter electrode layer (“CE”) 12 which serves as a storage layer for ions when the device is in the bleached or clear state; and two transparent conductive layers (“TCLs”) 11 and 15 which serve to apply an electrical potential to the electrochromic device. Each of the aforementioned layers is typically applied sequentially on a substrate 16. Such devices typically suffer from intrinsic electronic leakage (between the electrochromic stack layers) and electronic breakdown.
Typically, electrical power is distributed to the electrochromic device through busbars. FIG. 2 illustrates the electrochromic device of FIG. 1, in cross-section, having power supplied from two conductive elements, such as busbars 18 and 19. In order to prevent the busbars from shorting together, the busbars are electrically isolated from one another. Conventionally, this is done by scribing the TCLs 11 and 15. As shown in FIG. 2, the first (lower) TCL 15 is scribed at point P1, making the lower TCL 15 a discontinuous (i.e., physically separate) layer, and thereby preventing the busbars from shorting across the lower TCL 15. The width of the scribe at point P1 is typically on the order of 25 microns or wider, while the length varies based on the width the particular device being formed. Similarly, the second (upper) TCL 11 is scribed at point P3, making the upper TCL 11 also discontinuous, and thereby preventing the busbars from being shorted together across the upper TCL 11. Similar to the dimensions of the P1 scribe, the P3 scribe is typically on the order to 25 microns or wider, while the length varies based on the width the particular device being formed.
An intrinsic property of the EC layer 14 is that it becomes conductive when it transitions to a colored state. In other words, inserting electrons and charge compensating ions (such as lithium ions) into the EC material 14 leads to the material transitioning from an insulating state to a conductive state. This transition can happen upon the inserted (or “intercolated”) electrons or charge compensating ions reaching a threshold concentration, whereupon the EC device transitions suddenly to a conductive state. Under ideal operation of the EC device, insertion of the charge compensating ions will not occur above the P1 scribe itself, as no electric field is generated there due to the absence of the lower transparent conductive layer. However, it is possible that charge compensating ions can migrate laterally (i.e., sideways in FIG. 2) in the layer according to the usual laws of diffusion. Moreover, when a threshold concentration of charge compensating ions migrate laterally into a material, the material becomes conductive. The distance that the threshold concentration of charge compensating ions are capable of diffusing laterally will hereinafter be termed the “migration length.” Should the migration length meet or exceed the P1 scribe width, a conductive region can form in the area of the P1 scribe. Furthermore, if the conductive region extends across the full width of the P1 scribe, the two portions 15a and 15b of the lower TCL 15 may be conductively connected by the conductive region. For example, as shown in FIG. 3, the portion of the EC layer 14 may be colored for a reasonable amount of time. During this time, lithium can diffuse laterally across the P1 scribe, converting the EC layer 14 in that area 17 from an insulating layer to a conducting layer. If the scribed channel between the two portions 15a and 15b of the lower TCL 15 is not wide enough, current may pass between these portions, thereby electrically shorting the busbars 18 and 19 together. Moreover, once the leakage path is completed, the area 17 cannot simply be converted back from a conducting region to an insulating region, since clearing the electrochromic device 10 will not apply an electric field to that region of the device 10 in order for it to bleach (i.e., transition from a colored state to a non-colored state or a less colored state).
Furthermore, in order to produce electrochromic devices in a more cost effective manner, it is necessary to modify the deposition process to provide for higher yields and to be more amenable to mass production. In general, the yield can be considered to be reduced every time a substrate or other workpiece is cycled between vacuum and atmosphere and vice versa. It is believed that this may be caused by dust and debris from the coating process, which is inevitably present in sputtering and which may be ‘blown’ around during venting and pumpdown, finding its way onto the active layers, leading to potential defects in the film structure, such as short circuits or “shorts.” Thus, depositing all of the layers in one single continuous vacuum step, i.e., one coating machine, would achieve a high yield. However, to produce the structure shown in FIG. 3, depositing all the layers in a single vacuum step would require including a laser scribe (or cut of some type) between the deposition of the lower transparent conductor and the deposition of the second transparent conductor in the same vacuum system. Such cutting processes are very difficult in a vacuum system. For instance, with regard to laser scribing, it is necessary to maintain an extremely tight focus for the laser. Such focus is very difficult to achieve efficiently with the mechanical tolerances present in typical commercial sputtering systems.
It is desirable to reduce the amount of electronic leakage between the portions of the transparent conducting layers of the electrochromic device while maintaining as high a yield as possible (e.g., conducting as few scribing steps during the cutting process as possible).